15 research outputs found
Hafnium Amidoquinoline Complexes: Highly Active Olefin Polymerization Catalysts with Ultrahigh Molecular Weight Capacity
The preparation and characterization of a new class of
polyolefin procatalysts is described. Hafnium tribenzyl procatalysts,
supported by amidoquinoline ligands, were prepared in two steps from
commercially available materials. Solid-state structures, determined
by single-crystal X-ray analyses, revealed that all the hafnium complexes
display approximate trigonal-bipyramidal geometry around the metal
center. The complexes were evaluated in an ethylene/1-octene copolymerization
study and were found to be highly active at elevated temperatures
(120 °C). The best catalyst, derived from ((2,6-dimethylphenyl)Â(2,4-dimethylquinolin-8-yl)Âamino)Âtribenzylhafnium
(<b>6d</b>), compares favorably to previously reported systems
supported by bidentate nitrogen-based ligands. In particular, this
catalyst exhibits very high molecular weight capacity and high catalytic
activity, with a moderate 1-octene response. Alkyl substitution at
the carbon <i>ortho</i> to the quinolino nitrogen was found
to be an important factor for improving polymer compositional homogeneity,
as evidenced by a narrowing of the polydispersity index and a single
melting temperature in the resulting copolymer
Copolymerization of Ethylene and 1,4–Pentadiene: Structure Characterization and Reaction Mechanism
Copolymerization of ethylene and 1,4-pentadiene was conducted
by
using a homogeneous catalyst to understand the insertion mode of 1,4-pentadiene.
The polymer microstructure of the synthesized material was subjected
to structural characterization using quantitative NMR spectroscopy,
diffusometry, two-dimensional correlation spectroscopy, and selectively
refocused insensitive nuclei enhanced by polarization transfer (Sel-RINEPT).
The multimodal NMR characterization allows effective differentiation
of chain ends and backbone signals, filters irrelevant spectral information,
and provides site-specific information to achieve unambiguous structural
elucidation. The experimental results reveal that pentadiene has been
primarily converted to cis- and trans-dialkyl-substituted cyclohexane moieties along the polymer backbone
over the course of polymerization. The analysis also confirms that
unreacted pendant allyl groups from pentadiene remain at a concentration
that is significantly lower than the cyclic structures. In comparison
to the literature results, some discrepancies in structural assignment
have been identified and the results will be discussed. Detailed molecular
structure elucidation provides critical insights into advancing the
understanding of the reaction mechanism
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior
Synthesis and Scale-up of Imino–Enamido Hafnium and Zirconium Olefin Polymerization Catalysts
New imino–enamido hafnium
and zirconium trimethyl complexes
were prepared in high yield by reacting a mixture of an imino–enamine
ligand and hafnium or zirconium tetrachloride with four equivalents
of methylmagnesium bromide in toluene. A significantly improved imine
formation reaction in the final step of the ligand synthesis was developed
that involves the reaction between the keto–enamine and a reagent
formed <i>in situ</i> by mixing 0.55 equivalents of titanium
tetrachloride and 5.5 equivalents of <i>n</i>-butylamine.
Ethylene/1-octene polymerization evaluations at 120 °C revealed
that polymerization characteristics of the imino–enamido hafnium
and zirconium trimethyl derivatives were very similar to those of
the tribenzyl analogues. A scale-up of the hafnium trimethyl derivative,
performed on a 255 g scale, was accomplished in an overall yield of
57% in four steps starting with commercially available cyclohexa-1,2-dione.
Hafnium and zirconium complexes derived from two isomeric imino–enamine
ligands each resulted in very high molecular weight ethylene/1-octene
copolymers, which differ significantly, however, in the level of incorporated
octene. These features make these new catalysts good candidates for
the preparation of olefin block copolymers via chain-shuttling polymerization
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior
Synthesis and Scale-up of Imino–Enamido Hafnium and Zirconium Olefin Polymerization Catalysts
New imino–enamido hafnium
and zirconium trimethyl complexes
were prepared in high yield by reacting a mixture of an imino–enamine
ligand and hafnium or zirconium tetrachloride with four equivalents
of methylmagnesium bromide in toluene. A significantly improved imine
formation reaction in the final step of the ligand synthesis was developed
that involves the reaction between the keto–enamine and a reagent
formed <i>in situ</i> by mixing 0.55 equivalents of titanium
tetrachloride and 5.5 equivalents of <i>n</i>-butylamine.
Ethylene/1-octene polymerization evaluations at 120 °C revealed
that polymerization characteristics of the imino–enamido hafnium
and zirconium trimethyl derivatives were very similar to those of
the tribenzyl analogues. A scale-up of the hafnium trimethyl derivative,
performed on a 255 g scale, was accomplished in an overall yield of
57% in four steps starting with commercially available cyclohexa-1,2-dione.
Hafnium and zirconium complexes derived from two isomeric imino–enamine
ligands each resulted in very high molecular weight ethylene/1-octene
copolymers, which differ significantly, however, in the level of incorporated
octene. These features make these new catalysts good candidates for
the preparation of olefin block copolymers via chain-shuttling polymerization
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior
Preparation of New Olefin Polymerization Precatalysts by Facile Derivatization of Imino–Enamido ZrMe<sub>3</sub> and HfMe<sub>3</sub> Complexes
A novel
strategy for polyolefin catalyst development was explored, in which
imino–enamido zirconium and hafnium trimethyl complexes were
used as synthons to produce a diverse array of new dimethyl derivatives.
Specifically, reactions of the trimethyl precursors with protic reagents
(i.e., imidazolimines, phosphinimines, and phenols) or unsaturated
organic reagents (i.e., diisopropyl ketone and diisopropylcarbodiimide)
resulted in the formation of new complexes wherein a single methyl
group is replaced by a heteroatom-based ligand. In total, ten new dimethyl
complexes were prepared and isolated in high yields utilizing these
synthetic approaches. The new complexes were evaluated as precatalysts
in ethylene/1-octene copolymerization reactions at 120 °C. Seven
complexes were found to be competent catalysts under these conditions,
and the resulting copolymers comprised a wide range of molecular weights
and octene contents. The best catalysts of the series comprised imino–enamido
complexes containing a phosphine-imidato ligand, which exhibited remarkably
high activities, had high ethylene selectivities, and produced ethylene/1-octene
copolymers with exceptionally high molecular weights. This work demonstrates
that the replacement of one of the alkyl groups from trialkyl complexes
can be a very effective approach for accessing a variety of new dialkyl
precatalysts that can exhibit diverse polymerization behavior